Method of improving performance of gas-liquid separators

ABSTRACT

The performance of gas-liquid separators used to separate a liquid from a mixture containing at least one liquid and at least one gas, is enhanced by injecting into the mixture an additive, such as a suitable polymer, capable of imparting viscoelastic properties to the liquid. Suitable separators are those wherein crude oil is separated from a mixture obtained from an underground oil reservoir, the mixture typically containing water, hydrocarbon oil and gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed to a method for improving performance ofgas-liquid separators. More particularly, the invention is directed to amethod of improving the operation of gas-liquid separators whichseparate hydrocarbonaceous liquids, e.g., crude oil, from gas, such asgas contained in the stream of crude oil produced from an undergroundreservoir.

2. Description of Related Art

In many industrial applications, it is necessary to separate a liquidconstituent of a mixture from the gaseous constituent thereof. Forexample, crude oil, which is produced from underground reservoirs as amixture of oil, water and hydrocarbon gases (natural gases), must beseparated from the water and gases before it is subjected to downstreamprocessing and upgrading. The natural gas normally consists of a mixtureof strength chain or paraffin hydrocarbon gases plus lesser amounts ofcyclic and aromatic hydrocarbons. The gas stream may also consist ofsmall quantities of CO₂, H₂ S, mercaptans and H₂.

Different devices are known in the art which separate such entrainedgases from liquid hydrocarbons, as illustrated in "Fundamentals of Oiland Gas Separation", by C. R. Sivalls in Proceedings of the GasConditioning Conference, University of Oklahoma, Mar. 7-9, 1977, and inFundamentals of Natural Gas Conditioning by R. N. Curry, PennWellPublishing Company, 1983, and in the patent literature. For example,McMillan, U.S. Pat. No. 4,424,068, discloses a separator for separatinga mixture of oil, gas and water received from a hydrocarbon-producingwell. The separator comprises a vessel containing a dynamic separatordevice followed by separation chambers. The dynamic separator deviceprogressively increases the droplet size of the oil and water of themixture by flowing it in a spiral. Subsequently, the mixture is forcedto flow linearly into the first of a series of the separation chambers,wherein the mixture is impacted against an impact member to partiallyseparate the gas from the resultant oil and water mixture. The partiallyseparated gas is processed separately from the resulting mixture ofwater and oil. An unspecified treatment chemical may be admixed with themixture to enhance the separation of the constituent components of themixture from each other.

Other three-phase oil-gas-water separators are also known in the art.For example, typical horizontal and vertical three-phase oil-gas-waterseparators are disclosed by H.V. Smith in Petroleum Production Handbook,Volume I, Chapter 11, McGraw-Hill Book Company, Inc., New York (1962),edited by T. C. Frick and R. W. Taylor, the entire contents of Chapter11 being incorporated herein by reference.

Rivers, Jr., et al., U.S. Pat. No. 4,132,535, disclose the use of acopolymer of an alkene-substituted pyridinium group and analkene-substituted benzene group, such as a copolymer of styrene and2-vinyl pyridine, in gas streams to control the formation of oil andwater emulsions and hydrates.

SUMMARY OF THE INVENTION

The separation of a liquid from a mixture comprised of at least one gasand at least one liquid in a gas-liquid separation apparatus means inenhanced by injecting into the mixture at least one additive capable ofimparting viscoelastic properties to the liquid in the mixture. If themixture comprises a hydrocarbon and an aqueous liquid, two differentadditives are injected into the mixture, one of such additives beingsoluble in the hydrocarbon liquid and the other in the aqueous liquid.

If the mixture comprises only one hydrocarbon liquid, the additiveinjected into the mixture must be soluble in the hydrocarbon liquid. Ifthe mixture comprises several hydrocarbon liquids, the additive injectedinto the mixture must be soluble in all of the hydrocarbon liquids.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph of the relationship between the Screen Factor andFilament Index for the data of Example I.

FIG. 2 is a graph of the relationship between the Screen Factor andFilament Index for the amount of the Conoco CDR-102 additive in aStatfjord crude for the data of Example I.

FIG. 3 is a graph of the relationship between the Column Height and theScreen Factor for the Statfjord crude containing the Conoco CDR-102additive (Example I).

FIG. 4 is a graph of the relationship between the Screen Factor and theFilament Index for the water solution containing the Dowell J431additive (Example II).

FIG. 5 is a graph of the relationship between the Screen Factor and theamount of the J431 additive of the water solution (Example II).

FIG. 6 is a graph of the relationship between the Screen Factor and theColumn Height of the water solution containing the Dowell J431 additive(Example II).

DETAILED DESCRIPTION OF THE INVENTION

The liquid to be separated from the mixture of liquid and gases inaccordance with the present invention is any liquid which is an aqueousphase or a non-aqueous phase, an example of the former being a formationbrine, and an example of the latter being a crude oil.

More than one gas-liquid separator vessel in series may be used in theprocess of this invention. In such a case, it may be necessary to injectthe additive between the consecutive vessels, depending upon the natureof the liquid, the mixture thereof with the gas and other processconditions, as will be apparent to those skilled in the art. Althoughthe method of the present invention can be practiced with any knownseparator means, it is particularly suitable for enhancing theperformance of crude oil-gas separators, such as that described by H. V.Smith on pages 11-17 of Petroleum Production Handbook, cited above.

Thus, in the preferred embodiment, the method of the present inventionis directed to gas-liquid separators used to separate crude oil from amixture thereof with water and gas. Accordingly, the invention will bedescribed herein in conjunction with the use thereof in a crude oilseparator means. However, it will be obvious to those skilled in the artthat the process is not limited to that particular application and thatit can be used in any gas-liquid separator means.

As is known to those skilled in the art, crude oil recovered fromunderground formations is usually recovered in the form of mixturescontaining the crude oil, gas, comprised mostly of hydrocarbons, andwater. According to the method of the present invention, the operationof such gas-liquid separators is modified by injecting at least oneadditive into the stream of the mixture of the crude oil, water and gasbefore the introduction thereof into the gas-oil separator orsimultaneously therewith. The additive is injected to impartviscoelastic properties to the liquid. Without wishing to be bound byany theory of operability, it is believed that the liquids having suchviscoelastic properties generate substantially reduced amounts of mistas compared to the same liquids containing no additives. The liquidswithout the additives, it is believed, exhibit Newtonian liquidcharacteristics or purely viscous, i.e., non-viscoelastic, flowproperties. The mist is normally generated by the impingement of theentering stream of the mixture on the internal portions of thegas-liquid separators, collision of droplets, liquid blow-off fromsurfaces, pressure changes and bubble collapse within the gas-liquidseparators. The misting is undesirable because it can adversely affectseparator efficiency. The production-limiting entrainment of oil andwater in the form of fine liquid particulates (mist) in the gas streamin the separator is a particularly costly problem. In conventional priorart separator technology, a mist extractor or eliminator, such as wovenwire mesh or ceramic packing, was located near the gas outlet tocoalesce the small liquid particles that did not settle out. Suchtypical particles have the same size range of about 40 to about 500microns.

In the practice of the invention, the mixture recovered from theunderground oil-containing formation is conducted to a conventionalliquid-gas separator. Prior to the introduction of the mixture into theseparator or simultaneously therewith, there is injected into themixture a t least one additive capable of imparting viscoelasticproperties to the hydrocarbon liquid. If water is present in such aliquid, a water-soluble additive is also added simultaneously with orsubsequently to the addition of the first additive into the mixture solong as the water-soluble additive is introduced before orsimultaneously with the introduction of the mixture into the separator.The rate of the addition of the two additives depends on the amount ofthe water and the crude oil in the mixture. The addition of the twoadditives into the mixture reduces the amount of misting produced insideof the gas-liquid separator means. The amount of the additive requiredto impart viscoelastic properties to the liquid will depend, as will beapparent to those skilled in the art, on the nature of the liquid andthe relative amount thereof in the mixture to be treated. In thisconnection, the term "viscoelastic properties" is used herein todesignate a combination of unusual rheological phenomena superimposed onwhat superficially appears to be simple Newtonian fluid according to aclassical viscosity determination. The characteristics of viscoelasticliquids are discussed in published references, such as: Rheometry, K.Walters, Champman and Hall/John Wiley Pub. 1975, Dynamics of PolymericLiquids, R. B. Bird, R. C. Armstrong, and O. Hassager, J. Wiley and SonsInc., Pub. 1977, "Flow of Non-Newtonian Fluids", A. B. Metzner, inHandbook of Fluid Dynamics, McGraw-Hill Co., Inc., 1961, andViscoelastic Properties of Polymers, J. D. Ferry, Wiley Publishing Co.,1961, the contents of all of which are incorporated herein by reference.

One of the methods of detecting the presence of viscoelastic behavior ina liquid, especially dilute (relatively liquid), involves the use of theDow Screen Viscometer. The Dow Screen Viscometer consists of acapillary-type viscometer fitted with a series of fine mesh screens, asdescribed in detail by MacWilliams, et al., "WATER SOLUBLE POLYMERS INPETROLEUM RECOVERY", Water Soluble Polymers, N. M. Bikales, editor,Plenum Press, New York, 1973, the entire contents of which areincorporated herein by reference. Briefly, in the Dow Screen Viscometer,the alternating converging/diverging flow field through the mesh of eachscreen produces a "non-viscometric" flow which is response to thepresence of viscoelasticity in dilute solutions. Results of the screenviscometer tests are reported as "Screen Factor", which is the ratio ofthe flow time of the liquid containing the additive to the flow time ofthe untreated liquid. Thus, a sufficient amount of the hydrocarbon-and/or water-soluble additive or additives is injected into the mixtureto cause the mixture to have a Screen Factor of about 3 to about 65,preferably about 5 to about 50 and, most preferably, about 5 to about30. Dilute viscoelastic solutions (i.e., mixtures containing theadditive or additives) of the type considered here will be characterizedby a Screen Factor larger than the relative viscosity ratio, defined asthe viscosity of liquid plus additive divided by the viscosity of theuntreated liquid. Such viscoelastic solutions will have the values ofScreen Factor which are at least 1.4 times the relative viscosity ratio.A solution containing 100 parts per million by weight (wppm) of anadditive characterized by high molecular weight and high flexibilitycan, as a consequence of its viscoelastic properties, be characterizedby a Screen Factor and order of magnitude or more larger than theviscosity ratio. Generally speaking, for a given concentration, thehigher the molecular weight the higher the Screen Factor. In addition tomolecular weight and concentration, the Screen Factor is also affectedby molecular structure parameters and solubility effects.

Another device which can be used to determine the viscoelasticproperties of the liquid and, therefore is useful in evaluating theefficacy of the additives, is the "Ductless Siphon", described by Penget al., in "PRELIMINARY INVESTIGATION OF ELONGATIONAL FLOW OF DILUTEPOLYMER SOLUTIONS", JOURNAL OF APPLIED PHYSICS, Vol. 47, p. 4255 (1976),the entire contents of which are incorporated herein by reference. Thisapparatus, in use, approximates an elongational flow, and thus can beused to detect the filament-forming effect dominated by liquidelasticity and elongational viscosity. The results of testing in theDuctless Siphon are reported in terms of "Column Height" which is theheight of rise of an unsupported column from a quiescent pool into theopening of a capillary. If the Ductless Siphon is used to test theproperties of the mixture containing hydrocarbon- and/or water-solubleadditive or additives, the Column Height of such a mixture must be about0.5 to about 35, preferably about 1 to about 25, and most preferablyabout 1 to about 15 centimeters (cm).

If more than one additive is injected into the mixture to impartviscoelastic properties to the water contained in the mixture and to thecrude oil, the amount of each additive injected into the mixture iscontrolled separately to impart to both, the water and the crude oil,the viscoelastic properties as discussed above.

Various hydrocarbon-soluble additives that impart drag reducing andviscoelastic properties which can be used in accordance with the presentinvention have a molecular weight of about 0.4×10⁶ to about 50×10⁶,preferably about 1×10⁶ to about 30×10⁶ and most preferably about 1×10⁶to about 15×10⁶. The additives include such materials aspolydimethylsiloxane resins having a structure comprising ##STR1##characterized by viscosity average molecular weight of about 0.8×10⁶ toabout 30×10⁶ described by Canevari et al, U.S. Pat. No. 3,493,000, madeby processes referenced by Lichtenwalner and Sprung, "Silicones", in N.M. Bikales, Executive Editor, Encyclopedia of Polymer Science andTechnology, Interscience Publishers, 1967, Chapter 12; copolymers ofethylene and propylene, disclosed by Seymour et al, U.S. Pat. No.3,559,664, and the Netherlands Published Application No. 6,813,862, theentire contents of both being incorporated herein by reference; aluminumsalt of an alkyl phosphate ester, as disclosed by Crawford et al, U.S.Pat. No. 3,757,864, also discussed by Sylvester et al in "TheConcentration and Friction Velocity Effects on Drag Reduction byDowell-APE in Kerosene" Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 1,1979, pages 47-49, the contents of both being incorporated herein byreference; homopolymers or copolymers of alpha-olefin monomers havingfrom 6 to 20 carbon atoms having a molecular weight of from 1 to 40million, disclosed by Culter et al, U.S. Pat. No. 3,692,676, the entirecontents of which are incorporated herein by reference; homopolymers andcopolymers of derivatives of acrylic acid, methacrylic acid, or styrene,disclosed in German Published Application No. 2,056,700, the entirecontents of which are incorporated herein by reference; and two blockcopolymers consisting of a block A, substantially soluble in thehydrocarbon phase having an average molecular weight of between 50,000and 20 million, and a block B, substantially less soluble in thehydrocarbon phase, having average molecular weight between about 500 and5 million, as disclosed by Kruka et al, U.S. Pat. No. 3,687,148 andSeymour et al, U.S. Pat. No. 3,682,187, the entire contents of bothbeing incorporated herein by reference.

Various water-soluble additives that impart viscoelastic and dragreducing properties which may be employed in carrying out the presentinventions have a molecular weight of about 0.4×10⁶ to about 50×10⁶,preferably about 1×10⁶ to about 30×10⁶, and most preferably about 1×10⁶to about 15×10⁶. The water-soluble additives include copolymers ofacrylamide and dimethyl diallyl ammonium chloride or diallyl ammoniumcompounds, with and without cross-linking by N-N methylenebisacrylamide, disclosed in U.S. Pat. No. 3,562,226; copolymers ofacrylamide and N-N methylenebisacrylamide, disclosed in Canadian Pat.No. 791,202; acrylic acid-acrylamide diacetone acrylamide terpolymer,disclosed in U.S. Pat. No. 3,537,525; copolymers of2-acrylamido-2-methylpropane sulfonic or its water-soluble salt andacrylamide, having molecular weight of at least 1 million, disclosed inU.S. Pat. No. 3,768,565; polyethylene oxide polymers, disclosed in U.S.Pat. No. 3,289,623; monoalkenyl aromatic sulfonate polymers, disclosedin U.S. Pat. No. 3,023,760; polyacrylamide polymers disclosed in U.S.Pat. Nos. 3,102,548 (Smith et al) and 3,254,719; and, acrylicacid-acrylamide-diacetone acrylamide terpolymer disclosed in CanadianPat. No. 876,020 (Sarem). The entire contents of all of theabove-identified patents disclosing water-soluble polymers areincorporated herein by reference.

In general, additives which can be used in this invention are suchadditives which: are readily dispersible in the liquid phase, i.e., thecrude oil or water; produce an additive-liquid combination characterizedas having "viscoelastic" properties, as evidenced by the test resultsobtained with the Screen Viscometer, Ductless Siphon, or similardevices; have substantially no adverse effect on downstream processingof the liquids or the gases; and are not characterized by a narrowdistribution of molecular weight.

As will be apparent to those skilled in the art, the exact compositionof an additive package for mist suppression will depend upon thecharacteristics of the crude oil, the chemistry of the water producedwith the oil, separator operating conditions, characteristics of theadditives and logistic requirements. The mist suppression additivespackage may also include materials which support and/or enhance theviscoelastic/suppression activity by providing such vital functions assacrificial adsorption, defoaming action, oxygen scavenging andmaintenance of proper water chemistry. For example, in the event a waxycrude is recovered from the underground formation, it may be necessaryto include an agent, such as a pour point depressant, which ispreferentially interacted with the wax crystals to minimize undesirabledepletion of the mist suppressor. If the crude recovered from theunderground formation is a foamy crude, it may be necessary to add adefoamer to the package of additives to minimize the contribution offine liquid particulates (mist) from this source.

If the mixture of the liquid and the gases to be treated contains water,it may be necessary to adjust water chemistry to minimize precipitationof the additive. For example, it is known that certain polyacrylamidestend to precipitate in the presence of divalent ions. Therefore, if sucha polyacrylamide were to be used, the divalent ions would have to beinitially removed or complexed and, possibly, pH adjusted to minimizeoxidative degradation.

It is also important in practising the present invention to minimizepremature shear degradation of the additive which may result from mixingthe additive with the liquid, e.g., in the injection pump, or at pointsof sudden expansion or contraction within the injection piping system.Shear degradation of such additives can be minimized in a manner knownto those skilled in the art. For example, the possible shear degradationof water-soluble additives can be minimized by injecting the form of aheated slurry consisting of undispersed additives suspended in anon-interacting carrier liquid, as taught in U.S. Pat. No. 3,435,796.According to the teachings of that patent, micron-sized polymerparticles are rendered inert while dispersed in a hot carrier phase andsubsequently activated to produce essentially unsheared polymer whenintroduced to a cool aqueous phase just prior to the injection thereofinto the separator. Another means of minimizing the shear degradation isdisclosed in U.S. Pat. No. 3,601,079. Alternatively, an emulsion of thepolymer may be employed wherein a high concentration of unswollen(inert) polymer particles is suspended in an emulsion which issubsequently broken up just prior to the injection into the mixture ofthe gas and the liquid.

As discussed above to some extent, the water-soluble and thehydrocarbon-soluble additives of the present invention are injected intothe mixture separately, and they are amenable to process controloperations. Therefore, remote control of separator performance ispossible by a suitable system injecting the additive mix upon thereceipt of a signal from a mist-detecting transducer or other suitabledevices, e.g., a nuclear densitometer, within the liquid-gas separator.As will be apparent to those skilled in the art, any other methods ofinjecting the additives of the present invention are also contemplatedherein.

The following Examples further illustrate the essential features of theinvention. However, it will be apparent to those skilled in the art thatthe specific reactants and reaction conditions used in the Examples donot limit the scope of the invention.

Before illustrating this invention with specific examples, it isdesirable to describe how the atomization experiments were performed.Baseline tests were performed on additive-free liquids as follows:liquid was converted to mist in an apparatus consisting of an atomizerfitted with a gas (nitrogen) supply and controls to provide constantliquid feed rate but different gas/liquid ratios. This flow system wasenclosed in a transparent chamber where the spray was photographed usinga high intensity electronic flash to "freeze" the pattern.

For the baseline conditions selected, untreated liquid was ejected fromthe atomizer in the form of a mist comprised of liquid droplets.Untreated liquid did not produce a measurable Column Height in theductless siphon test. The efflux time through the screen viscometer ofuntreated liquid was recorded for interpretation of results with treatedliquid.

The atomization tests were then repeated with liquids containingadditives known to impart viscoelastic properties and an additive knownfor its anti-foaming qualities. As will be seen, effective additivessubstantially reduced mist formation. Fine liquid droplets were replacedby mixtures of liquid filaments. Analysis of the photographic recordsshowed that as additive concentration increased, the morphology of theliquid ejected from the atomizer changed in the following order: liquiddrops--multiple short filaments--multiple long filaments--monofilaments.These results were interpreted in terms of a "Filament Index" in whichan injection of droplets was given a rank of zero and an injection ofmonofilaments was given a rank of 10. The onset of mist suppression istaken as a Filament Index of the order of 1.

Since these additives are subject to shear degradation during the ScreenFactor and ductless siphon tests, Screen Factor, Column Height andviscosity were determined on aliquots of treated liquids prior to theatomization experiments.

All of the materials employed in the examples are known for their "dragreducing" qualities. Drag reduction in hydrocarbon liquids with ConocoCDR is discussed by Burger, E. D., et al, in "Studies of Drag ReductionConducted Over a Broad Range of Pipeline Conditions When Flowing PrudhoeBay Crude Oil", Trans. Society of Rheology, Vol. 24, p. 603, 1980. Thedrag reducing characteristics of Dowell polyacrylamides and UnionCarbide polyethylene oxides are cited by P. S. Virk, "Drag ReductionFundamentals", AIChE Journal, Vol. 21, p. 625, 1975. Additive-liquidcharacteristics and conditions required for optimum drag reducingcharacteristics, e.g., high molecular weight, low molecular rigidity,high ratio of molecular weight to critical chain entanglement molecularweight, and good solvent qualities (as opposed to theta solventqualities) are discussed by G. Liaw, J. L. Zakin, and G. K. Patterson,"Effects of Molecular Characteristics of Polymers on Drag Reduction",AIChE Journal, Vol. 17, p. 391, 1971. For an example of an applicationof drag reduction, see J. G. Savins, "Method of Decreasing Friction Lossin Turbulent Flow", U.S. Pat. No. 3,361,213 (1968).

Examples I and Examples II-III illustrate the invention with materialsproducing viscoelastic effects and suppressing mist production inhydrocarbon and aqueous media, respectively. Example IV illustrates theresults obtained with a non-viscoelastic anti-foaming type additive.

EXAMPLE I

The atomization tests described above were performed with a bath ofStatfjord crude oil treated with different concentrations of an additivereferred to here as "Conoco CDR-102" obtained from Conoco, Inc.,Houston, Tex. It is thought that the additive is a high molecular weightpolyolefin, such as that taught in U.S. Pat. No. 3,692,676, issued Sept.10, 1972, which discloses the preparation and use of small quantities ofvery high molecular weight polyolefins to reduce friction losses ofhydrocarbon liquids flowing through conduits.

The results are summarized in FIGS. 1-3. The baseline atomizationcondition where only droplets are produced is indicated in FIG. 1 byFilament Index and Screen Factor values of 0 and 1, respectively.

The correlation between Filament Index or mist suppression and ScreenFactor for this additive-liquid pair is illustrated in FIG. 1. Note thata significant change in the misting character of this hydrocarbon liquidresults on addition of Conoco CDR. The onset of mist suppression forthis additive-liquid pair corresponds to a Screen Factor of about 2.5.Multiple short filaments appear at a Screen Factor of about 3.0. At aFilament Index of about 4, corresponding to a Screen Factor of about 5,droplet production is significantly suppressed with spray morphologycharacterized by the ejection of multiple long filaments.

The correlation between Screen Factor and concentration is illustratedin FIG. 2. The onset of mist suppression occurs at about 50 wppmadditive, with suppression occurring over a broad range of additiveconcentration. Comparing FIGS. 1 and 2, significant mist suppressionresults between 100 wppm and 200 wppm. At 200 wppm, corresponding to ascreen factor of about 9, multiple long filaments are produced.

Column Height and Screen Factor are correlated in FIG. 3. This result issignificant, indicating the mist suppression effect is closely relatedto elongational viscosity properties that appear when the liquid isconverted to a viscoelastic liquid. The correlation also demonstratesthat either the ductless siphon or the screen viscometer can be used toscreen additives for application in the practice of this invention.However, the screen viscometer is a preferred experimental techniquebecause of the simplicity of design and operation.

EXAMPLE II

Similar atomization experiments were performed in aqueous media(deionized water) containing different concentrations of partiallyhydrolyzed poly(acrylamides) designated by Dowell as "J430", "J431", and"J432", available from Dowell, Inc., Tulsa, Okla.

Results obtained with the J431 additive are illustrated in FIGS. 4-6. Ingeneral, the trends and correlations are qualitatively similar to thoseobtained with the hydrocarbon soluble additives of Example 1. However,at a given concentration, the Conoco CDR-102 additive is more effectiveat suppressing misting in Statfjord crude than the J431 additive is insuppressing misting in water. Performance parameters for the J430 andJ432 additives are illustrated in Table I below.

                  TABLE I                                                         ______________________________________                                                                                Relative                                       Conc.    Screen  Column Filament                                                                             Viscosity                             Additive (wppm)   Factor  Ht     Index  Ratio                                 ______________________________________                                        J430      50      1.9     --     0      1.2                                   J432      50      1.7     --     0      1.3                                   J430     150      3.5     0.44   2      1.4                                   J430     300      6.9     1.06   7      3.8                                   J432     300      13.5    2.95   7      5.6                                   ______________________________________                                    

These results and those given in FIGS. 4-6 show for those additive-pairsthe onset concentration is above 50 wppm, and active mist suppressingsystems are characterized by a Screen Factor considerably larger thanthe corresponding relative viscosity ratio.

EXAMPLE III

Atomization experiments were performed with aqueous solutions containingdifferent concentrations of poly(ethylene) oxides designated by UnionCarbide Company, Danbury, Connecticut, as "N-12K", "N-60K", "WSR 301",and "Coagulant". These solutions contained 10 percent (wt.) isopropylalcohol to inhibit oxidative degradation of the additives. Typicalresults are summarized in Table II below:

                  TABLE II                                                        ______________________________________                                                  Conc.      Screen  Column   Filament                                Additive  (wppm)     Factor  Height   Index                                   ______________________________________                                        N-12K     50         1.86    0.25     0                                       N-60K     50         3.77    0.20     2                                       Coagulant 75         51.5    7.8      9                                       N-60K     150        6.0     0.45     5                                       Coagulant 200        62.8    14.3     9                                       N-12K     1200       10.2    1.98     9                                       WSR301    50         12.1    0.69     2                                       Coagulant 50         36.4    4.2      7                                       Coagulant 100        --      --       9                                       N-12K     150        3.1     0.2      2                                       WSR301    150        21.1    2.52     7                                       Coagulant 150        55.1    11.9     9                                       N-12K     300        4.8     0.44     5                                       N-60K     300        7.9     0.91     5                                       WSR301    300        29.4    5.2      9                                       N-60K     1200       18.5    --       9                                       ______________________________________                                    

These results, qualitatively similar to those shown in the precedingexamples, show that useful mist suppression effects can be obtained withpoly(ethylene) oxide derivatives.

Examples I-III illustrate the following:

(1) the onset concentration depends on the additive-liquid pair ofinterest, with active materials suppressing droplet formation atconcentrations of the order of 50 wppm.

(2) evidence of Screen Factor or Column Height activity is a validscreening criterion for predicting mist suppression activity,

(3) the magnitude of the Screen Factor and Column Height at the onset ofmist suppression will depend on the additive-liquid pair,

(4) preferred active mist suppressing systems are characterized by aScreen Factor at least about twice the relative viscosity ratio,

(5) the mist production is inhibited if a mixture or solution ischaracterized by a Screen Factor of at least about 5,

(6) significant mist suppression usually occurs between 50 wppm and 200wppm,

(7) effective mist suppression, without excessive relative viscosityratio, can result in a mixture or solution characterized by a ScreenFactor of the order of 25,

(8) an additive-liquid pair characterized by a Screen Factor of theorder of 50 is likely to totally suppress mist formation,

(9) mist suppression as disclosed in this invention is demonstrated inhydrocarbon liquids using high molecular weight polyolefins, and inaqueous media using molecular weight poly(ethylene) oxides and partiallyhydrolyzed poly(acrylamides),

(10) since the materials demonstrating mist suppression also exhibitdrag reducing characteristics, if follows that evidence of drag reducingbehavior in the process fluid of interest may be a valid criterion forpredicting mist suppression activity,

(11) characteristics and conditions considered desirable for optimumdrag reducing activity are also preferred for effective mist suppressionin the practice of this invention, e.g., high molecular weight, lowmolecular rigidity, high ratio of molecular weight to critical chainentanglement molecular weight, and good solvent qualities (as opposed totheta solvent qualities).

EXAMPLE IV

Atomization experiments were performed with batches of Statfjord (S) andHigh Island (HI) crudes treated with an additive referred to herein as"Dow Corning 200", a known anti-foaming agent. The purpose of thesetests was to determine whether under the baseline atomization conditionsused herein anti-foaming activity would alter the morphology of liquidejected from the atomizer in a manner similar to that produced withviscoelastic additives. Table III below summarizes typical results ofthese tests with the Dow Corning product:

                  TABLE III                                                       ______________________________________                                                 Conc.    Screen    Column Filament                                   Crude    (wppm)   Factor    Height Index                                      ______________________________________                                        S        200      1.0       0.0    0.0                                        HI       200      1.0       0.0    0.0                                        ______________________________________                                    

Only data at the high concentration level of 200 wppm are presentedbecause the screen factor for the Dow Corning product was found to beunity (or close to it) and independent of concentration over the rangeinvestigated (up to 200 wppm). Treatment levels extended well beyond theconcentration required for good anti-foaming effectiveness. However, nomist suppression occurred, as evidenced by Filament Index values ofzero, because the defoamer did not impart viscoelastic properties tothese hydrocarbon liquids, as evidenced by Screen Factor and ColumnHeights of unity and zero, respectively. Thus anti-foaming quality isnot a sufficient condition for mist suppression as illustrated in thisExample.

It will be apparent to those skilled in the art that the specificembodiments discussed above can be successfully repeated withingredients equivalent to those generically or specifically set forthabove and under variable process conditions.

From the foregoing specification, one skilled in the art can readilyascertain the essential features of this invention and without departingfrom the spirit and scope thereof can adapt it to various diverseapplications.

We claim:
 1. A method of enhancing the separation, in a gas-liquidseparator means, of a liquid from a mixture comprising a gas and atleast one liquid comprising injecting into the mixture at least oneadditive imparting viscoelastic properties to the liquid, the amount ofthe additive being effective to cause the mixture to have a ScreenFactor of about 3.0 to about 65.0.
 2. A method of claim 1 wherein theamount of the additive is effective to cause the mixture to have aScreen Factor of about 5.0 to about
 50. 3. A method of claim 1 whereinthe amount of the additive is effective to cause the mixture to have aScreen Factor of above 5.0 to about
 30. 4. A method of claim 3 whereinthe Screen Factor of the mixture is at least 1.4 times the RelativeViscosity Ratio.
 5. A method of claim 4 wherein the amount of theadditive is effective to cause the mixture to have the Column Height ofabout 0.5 to about
 35. 6. A method of claim 5 wherein the amount of theadditive is effective to cause the mixture to have the Column Height ofabout 1.0 to about
 25. 7. A method of claim 6 wherein the amount of theadditive is effective to cause the mixture to have the Column Height ofabout 1.0 to about
 15. 8. A method of claim 7 wherein the mixturecomprises at least one hydrocarbon atom.
 9. A method of claim 8 whereinthe additive is a polymer having a molecular weight of about 400,000 toabout 50×10⁶.
 10. A method of claim 9 wherein the additive is a polymerhaving a molecular weight of about 1×10⁶ to about 30×10⁶.
 11. A methodof claim 10 wherein the additive is a polymer having a molecular weightof about 1×10⁶ to about 15×10⁶.
 12. A method of claim 11 wherein theadditive is selected from the group consisting of polydimethylsiloxaneof U.S. Pat. No. 3,493,000, copolymers of ethylene and propylene of U.S.Pat. No. 3,559,664, aluminum salt of a straight or branched chain alkylphosphate ester of U.S. Pat. No. 3,757,864, homopolymers or copolymersof C₆ -C₂₀ alpha-olefins of U.S. Pat. No. 3,692,676, homopolymers andcopolymers of derivatives of acrylic acid, methacrylic acid, or styrene,and two block copolymers consisting of a block A, substantially solublein the hydrocarbon liquid having an average molecular weight of between50,000 and 20 million, and a block B, substantially less soluble in thehydrocarbon liquid, having average molecular weight of between about 500and 5 million, of U.S. Pat. Nos. 3,687,148 and 3,682,187.
 13. A methodof claim 12 wherein the mixture comprises at least one aqueous liquid.14. A method of claim 13 wherein a second additive is injected into themixture, separately and independently from the first additive, thesecond additive being soluble in the aqueous liquid.
 15. A method ofclaim 14 wherein the second additive is a polymer having molecularweight of about 0.4×10⁶ to about 50×10⁶.
 16. A method of claim 15wherein the second additive is a polymer having molecular weight ofabout 1×10⁶ to about 30×10⁶.
 17. A method of claim 16 wherein the secondadditive is a polymer having molecular weight of about 1×10⁶ to about15×10⁶.
 18. A method of claim 17 wherein the second additive is selectedfrom the group consisting of copolymers of acrylamide and dimethyldiallyl ammonium chloride or diallyl ammonium compounds with or withoutcross-linking by N,N'-methylene bisacrylamide of U.S. Pat. No.3,562,226, copolymers of acrylamide and N-N methylenebisacrylamide,acrylic acid-acrylamide-diacetone acrylamide terpolymer of U.S. Pat. No.3,537,525, copolymers of 2-acrylamido-2-methylpropane sulfonic acid orits water-soluble salt and acrylamide of U.S. Pat. No. 3,768,565,polyethylene oxide polymers of U.S. Pat. No. 3,289,623,monoalkenylaromatic sulfonate polymers of U.S. Pat. No. 3,023,760,having the formula: ##STR2## wherein Ar is a divalent aromatic radicalselected from the group consisting of hydrocarbon radicals and nuclearchlorinated hydrocarbon radicals having its valence bonds on nuclearcarbon atoms;R is hydrogen or methyl; and M is a cation,polyacrylamidepolymers of U.S. Pat. Nos. 3,102,548 and 3,254,719, and acrylicacid-acrylamide-diacetone acrylamide terpolymer.